Fibroblast contractility and growth in plastic compressed collagen gel scaffolds with microstructures correlated with hydraulic permeability.

Scaffold microstructure is hypothesized to influence physical and mechanical properties of collagen gels, as well as cell function within the matrix. Plastic compression under increasing load was conducted to produce scaffolds with increasing collagen fibrillar densities ranging from 0.3 to above 4.1 wt % with corresponding hydraulic permeability (k) values that ranged from 1.05 to 0.03 μm², as determined using the Happel model. Scanning electron microscopy revealed that increasing the level of collagen gel compression yielded a concomitant reduction in pore size distribution and a slight increase in average fibril bundle diameter. Decreasing k delayed the onset of contraction and significantly reduced both the total extent and the maximum rate of contraction induced by NIH3T3 fibroblasts seeded at a density of either 6.0 x 10⁴ or 1.5 x 10⁵ cells mL⁻¹. At the higher cell density, however, the effect of k reduction on collagen gel contraction was overcome by an accelerated onset of contraction which led to an increase in both the total extent and the maximum rate of contraction. AlamarBlue™ measurements indicated that the metabolic activity of fibroblasts within collagen gels increased as k decreased. Moreover, increasing seeded cell density from 2.0 x 10⁴ to 1.5 x 10⁵ cells mL⁻¹ significantly increased NIH3T3 proliferation. In conclusion, fibroblast-matrix interactions can be optimized by defining the microstructural properties of collagen scaffolds through k adjustment which in turn, is dependent on the cell seeding density.